Truck drivers are disproportionately high users of the drug to help stay awake during long-haul routes. A 2003 study found that stimulants, including meth, were present in 4.1 per cent of drivers killed in traffic accidents on Australian roads. That figure rose to 23 per cent for truck drivers killed in accidents in the same period.

University of Sydney psychologist Dr David Bosanquet, put 15 self-admitted meth users and 15 "control" drivers in a car simulator over a 9km course that included rural, semi-rural and urban roads.

The results showed meth users averaged 4km/h faster than “normal” drivers, allowed for less distance to oncoming cars when making a right turn and weaved more both within the lane and when making lane changes.

His research is the first to clinically correlate methamphetamine drug use with driving behaviour. Past studies have used evidence based on crash reports to assess how drug use affects the ability to drive.

Dr Bosqanuet now wants government funding to research with larger numbers and eliminate the variables based on his small sample pool.

"We found that the dangerous driving of users was not associated with their blood levels of meth which varied widely. Instead their behaviours appear to be linked to long-term heavier use of meth as most of the drivers met the criteria for dependence,” Dr Bosqaneut said.

"This research was done for about $3000. I’d love to do a much bigger study into whether it is because of the drug use per-se, or whether it is because the personality of drug users also predisposes them to take risks.

"We can’t definitively say whether the driving performance of the meth-users group was affected by meth alone or in combination with other factors such as impulsivity. These factors were not teased apart because the small sample size made it too difficult to do so.”

"Taking small amounts can improve cognitive (brain) function because it has been shown to offset fatigue. Generally, when taken in large doses that effect is reversed - cognitive function decreases with dependence-based use of the drug.”

Methamphetamines are prescribed to people with attention deficit disorder or narcolepsy (people who suffer from “micro-sleeping”) to improve their concentration. The study notes meth increases brain function “giving the user feelings of energy, confidence, and euphoria and improved attention and cognitive function. However, meth can be a highly addictive drug, and chronic heavy use has been linked to neuroinflammation, neurodegeneration, cognitive impairment, and psychiatric symptoms including depression, anxiety, and psychosis”

Every Australian state tests for methamphetamine (such as ice and speed) use while driving but until now there has been no research evidence to support these policies and the related penalties.

“In 2004, Victoria was the first state in the world to introduce random roadside saliva testing for drug use including the methamphetamines, and since then all other Australian states have followed,” Dr Bosanquet said.

“In stark contrast to the wealth of research on drinking and driving safely there hasn’t been any clinical research comparing responses between heavily “drugged” meth users and non-drug-using drivers in lifelike driving scenarios.

“Since roadside drug testing was first implemented millions of dollars have been spent to test, charge, and sentence those found guilty. It's important to understand the science behind this sort of initiative and this is the first step,” Dr Bosanquet said.

Intriguingly, meth users crashed three times during the simulation compared to just one accident for the control group. Dr Bosqanuet said the wherabouts of the crashes on the course wasn't noted and the result wasn't statistically significant.

Example

Two US air force pilots who bombed Canadian troops on a training exercise during the 2002 Operation Desert Storm invasion of Iraq were on “speed” (Dexedrine) at the time. USAF documents show around 60 per cent of pilots were given 5mg of the drug during combat missions to improve their reaction times and alertness.

Dr Bosanquet’s research, published in the latest Psychopharmacology journal, states laboratory studies indicate the acute administration of amphetamines can sometimes enhance perceptual speed, vigilance, and psychomotor performance. Habitual use reverses those effects.